Burnside Rifle Company Model 1865 Spencer Repeating Carbine

Both Spencer and Burnside carbines were manufactured by the
Burnside Rifle Company. Spencer-manufactured models featured
six-groove rifling, while those made under contract by Burnside in
1865, as well as post-war armory conversions, used three-groove
rifling. Spencer carbines came into use in mid-1863 and by war's
end, they had become established as the dominant cavalry arm of the
Union Army. Spencers continued to see action on the frontier during
the Indian Wars. After the Civil War, Spencers were armory-modified
from their original .52 caliber to accept .50 caliber ammunition.
SN 14314